1. Field of the Invention
The present invention is related generally to rotor turning gears, and more specifically to apparatus for locking the lever that is used for engaging such rotor turning gears.
2. Statement of the Prior Art
Most large dynamoelectric machines, such as a steam turbine, are usually equipped with turning gears for rotating their rotors slowly during periods of warming up, cooling off, and particularly during shutdown periods of several days when it may be necessary to start the steam turbine again at short notice. The object of these turning gears is to maintain the rotor at approximately uniform temperatures circumferentially to assure that the rotor remains in a substantially straight, balanced condition.
Conventional turning gears generally comprise motor means for turning a gear train that is adapted for engagement with a coupling gear mounted on the rotor shaft. In order to engage and/or disengage the gear train from the coupling gear, turning gears typically include a lever that is pneumatically-operated between an engaged and a disengaged position. While these turning gears are engaged, the rotor shaft will turn at a prescribed speed. The turning gear will be automatically disengaged during start-up of the steam turbine when the speed of the rotor shaft increases above such prescribed speed.
One problem arising from these conventional turning gears is their inadvertent disengagement. That is, the speed of the rotor shaft being rotated by engaged turning gears may temporarily exceed the prescribed speed due entirely to an inadvertent source of energy such as a leakage of gland steam into the steam turbine. It can be readily appreciated, therefore, that such turning gears will prematurely disengage under these circumstances, in spite of the possibilities that the speed of the rotor shaft will undesirably be decreased on removal of the inadvertent source of energy.
A seemingly simple solution to this problem in prior art turning gears having engaging levers would be to lock such levers in place when their turning gear was engaged. However, the prior art has taught away from any approaches which would utilize engaging lever locks, since all turning gears must be capable of being automatically disengaged on demand.